Organic polymers having a modified surface and process therefor

ABSTRACT

Organic polymer surfaces are modified by contacting such surfaces with a haloester compound and a cationic compound of having a pK a  &gt;5. Preferably the organic polymer is selected from the group consisting of polyesters, aromatic polyamides, and graphitic polymers and the contacting is conducted at an elevated temperature.

This is a division of application Ser. No. 08/316,056 filed Sep. 30,1994 now U.S. Pat. No. 5,483,010 which is a continuation of applicaitonSer. No. 08/100,811 filed Aug. 2, 1993 now abandoned.

FIELD AND BACKGROUND OF INVENTION

The present invention relates to the modification of organic polymersurfaces and the articles produced therefrom. Particularly, theinvention relates to organic polymers having a surface modified toimprove the adhesive characteristics of such polymers.

It is well known in the art to surface treat organic polymers such aspolyesters to improve the utility of such polymers. For example, it isknown to treat polyester fibers to improve the adhesion of the polyesterto substances such as rubber in the manufacture of tires. In U.S. Pat.No. 4,054,634, multifilament polyethylene terephthalate yarn is treatedwith a two-part finish, one part of which is applied after spinning andone part of which is applied after drawing. The first part contains adefined polyoxyethylated-polyoxypropylated monoether whereas the secondpart contains the monoether in combination with a defined epoxy ethersilane and a sufficient amount of a water soluble alkaline catalyst toraise the pH to 8-10. Also see U.S. Pat. No. 4,348,517 wherein the sameepoxy ether silane is combined with the triglycidyl ether of a glyceroland a defined diglycidyl ether and is used as a fiber finish forpolyester yarn.

U.S. Pat. No. 3,793,425 also describes a process for improving theadhesion of polyester material to rubber. In the process, undrawnpolyester yarn is coated with a composition containing an epoxy resinwhich is preferably buffered with an alkaline agent, such as sodiumcarbonate, lithium carbonate, potassium carbonate or ammonium hydroxide.The use of epoxy resins with alkaline catalysts to improve the adhesionof polyester to rubber is further disclosed in U.S. Pat. Nos. 3,423,230and 3,464,878.

A process for treating chemically stabilized polyester material toimprove the adhesion of the polyester to rubber is also described inU.S. Pat. No. 4,751,143. As noted therein, the aging period forchemically stabilized, adhesive activated polyester material can bereduced by contacting the material before it is substantially drawn orstretched with a composition containing a defined epoxide compoundcatalyzed with ions of at least one of potassium, cesium, or rubidium ata pH of between about 7.5 to about 13.0.

The application of finishes to the polymer surface generally produces atemporary surface condition such as lubrication or electrostatic chargedissipation which may be removed when the surface is subsequentlyexposed to multiple processing steps. Additionally, polyester surfacemodifications of the prior art employing epoxies to improve the adhesionof polyester to rubber for example, have resulted in the creation oftoxic working conditions in the manufacture of such surface-modifiedpolyester or in the production of articles which in subsequentprocessing or use would expose individuals to toxic conditions.

Other approaches employed in art to adjust the characteristics orproperties of organic polymer surfaces include electrolytic and plasmatreatments. However, these processes are costly and have limitedprocessing rates. The application of a strong acid or base has not beenparticularly effective in modifying surfaces and can penetrate beyondthe surface, particularly in fiber structures, to cause strength loss.

Polyisocyanates have been employed to enhance adhesion in themanufacture of polyester yarns (see U.S. Pat. No. 3,549,740). Thesematerials have been applied at relatively high concentration levels(greater than 0.5 weight percent) and so generate obnoxious vapors,produce deposits on process rolls and bond filaments to filaments in theyarn bundle. Similar processing problems are encountered in theapplication of known polyester adhesives such as those based uponresorcinol-formaldehyde resins described in U.S. Pat. No. 3,660,202 andU.S. Pat. No. 3,318,750.

Molecular chains of aromatic groups connected by methylene groupsattached to carbon atoms in the benzene rings have been employed toenhance adhesion of polyester articles (see British PatentSpecifications 1,140,528 and 1,156,624). These products have been usedas an RFL additive for adhesions and not as individual components.However, it has been found that for such products to be effective, 1.5%of the weight of the yarn is required. At this level, the yarns bondtogether making the processing very difficult.

Accordingly, it would be desirable to have the capability to permanentlymodify the organic polymer surface employing a non-toxic process andimprove the processing of the organic polymer in the production ofarticles of manufacture.

SUMMARY OF INVENTION

By the invention an organic polymer having a modified surface isobtained, the surface modification is a result of the reaction between ahaloester compound having primary halogen substantially free ofhalohydrin and epoxy functionality and a coreactant comprising acationic compound of an acid having a pK_(a) >5, preferably reacted atan elevated temperature. As applied to polyester, polyetherimide,aromatic polyamide and graphitic polymers, the surface modificationimproves adhesion of such polymers to rubber and other elastomericmaterials.

DETAILED DESCRIPTION OF THE INVENTION

The invention is useful in conjunction with organic polymers generallybut has particular application to polyesters, aromatic polyamides, andgraphitic polymers to improve the adhesive characteristics of suchpolymers. Other suitable organic polymers include nylons, polyketones,polyetherketones, polyethylenes, polyphenylene sulfides and polyvinylalcohols.

The polyester employed in the present invention can be any polymericlinear ester which may be obtained by reacting one or more glycols ofthe series HO(CH₂)_(n) OH wherein n ranges from 2 to 6 with one or moredicarboxylic acids such as naphthalene dicarboxylic acid, 4,4'-diphenyldicarboxylic acid or, preferably, terephthalate acid. The polyester alsomay be prepared by alternate techniques such as polymerization of themonoester. The polyester can be a wholly aromatic polyester known to theart such as various combinations of p-hydroxybenzoic acid,2,6-hydroxynaphthoic acid, 2,5-hydroxynaphthoic acid,2,6-dihydroxynaphthalene, 2,6-naphthalenedicarboxylic acid, biphenol,bisphenol A, terephthalic acid, isophthalic acid and hydroquinone.Reference is made to U.S. Pat. No. 4,161,470, incorporated by reference,for a further description of such aromatic polyesters.

Additionally, the polyester may be reacted or blended with compatiblecompounds of polymers which do not substantially adversely affect thecharacteristics of the polyester. For example, compounds yieldingnon-ester linkages can be added into the reaction mixture for thepolyester or formed polymers, pigments, fillers, antioxidants, etc. canbe blended with the polyester. Preferably, polyester is polyethyleneterephthalate which has an intrinsic viscosity (IV) of at least 0.35 andwhen employed in the production of tire yarn or other industrialelastomeric applications has a preferred IV of at least 0.7 decilitersper gram. IV is the intercept at zero concentration of the plot in RV/Cvs C at 25° C. of polyester solutions in orthochlorophenol. RV is therelative viscosity and C is the concentration in grams per deciliter.

The graphitic polymers of this invention can be obtained by thecarbonization/graphitization of pitch, rayon or acrylonitrile polymerssuch as described in U.S. Pat. No. 3,775,520 and U.S. Pat. No.3,954,950, incorporated herein by reference thereto or by other methodsknown to the art. As described in the references the acrylonitrilepolymer is preheated, passed through a preoxidation heating zone havingan oxygen atmosphere and then passed through acarbonization/graphitization heating zone provided with an inertatmosphere. The invention is also applicable to aromatic polyamides suchas poly-paraphenylene terephthalamide,polyparaphenylene/3,4'-diphenylether terephthalamide andpolymetaphenylene isophthalamide.

The material into which the organic polymer is formed can be of any sizeand configuration amenable to surface modification processing. Thematerial can therefore be film, sheets, rods, filaments and the like. Asapplied to filaments for example, the material can be in the form ofyarns, cords and fabrics. As applied to filaments, the invention isparticularly applicable to those filaments which have been melt spun andquenched.

The haloester organic compounds of the present invention are reactive,preferably having primary halogens, and with the ester functionalityderived from primary alcohols. In particular, the haloester compoundsinclude aliphatic halohydroxyesters wherein hydroxy functionality aresecondary. The haloester compounds include those represented by theformula ##STR1## wherein R₁ may be H or C₁ -C₂₂ organic acid esterresidue; R₂ may be C₁ -C₂₂ organic acid ester residue; n is 0-10; m is1-4 and X is a halogen consisting of chlorine, bromine and iodine, thereis at lease one X; R₃ =organic residue of valence m.

The term "primary" means that the functionality is attached to aterminal aliphatic carbon. The term "secondary" means that the hydroxyfunctionality is attached to a nonterminal carbon contained in thealiphatic chain. The functionalities may be in the same or differentmolecules. Halogen is selected from the group consisting of chlorine,bromine and iodine and the haloester compound is substantially free ofhalohydrin and epoxy groups. As set forth in the parent application, theterm substantially free is set forth as the halohydrin value of lessthan or equal to 1.7% and the epoxy value of less than or equal to0.36%. As applied to the modification of the organic polymer surface forpurposes of improved adhesion, the preferred haloester organic compoundhas at least one chlorine in at least one group selected from --CH₂ C1group and a secondary hydroxyl. Such organic compounds can berepresented in the following formulas: ##STR2##

The coreactant can be any cationic compound of an acid having apK_(a) >5. Suitable coreactants include alkali metal, quaternaryammonium, quaternary phosphonium, and alkaline earth metal hydroxides,bicarbonates, carbonates, sulfites and oxides; also alkoxides,aryloxides, dimethylsulfoxide salts, acetamide salts, hydrocarbon salts,and hydrides. Preferred cationic compounds for improved adhesion arethose selected from the group consisting of quaternary ammonium andalkali metal hydroxides, carbonates, and bicarbonates.

The haloester organic compound and the coreactant are applied to theorganic polymer surface and preferably heated to a temperature of atleast 100° C. whereon the reaction occurs to produce a modified polymersurface. The application can be made as an emulsion or as a solutionwith the haloester organic compound and the coreactant appliedseparately or together but preferably together.

Although not to be limited thereto, the invention will hereafter bedescribed in a preferred embodiment. A polyester such as described inU.S. Pat. No. 4,414,169, incorporated by reference thereto, can beextruded as filaments and the filamentary material passed in thedirection of its length through a solidification zone wherein the moltenfilamentary material uniformly is quenched and is transformed to a solidfilamentary material.

In one aspect of the invention the haloester organic compound and thecoreactant can be applied as an emulsion or solution to the filamentarymaterial as it exits the solidification zone by known techniques such asvia a kiss roll, spray, foam, metered applicator, etc. In addition tothe haloester organic compound and the coreactant the emulsion maycontain other conventional constituents such as emulsifiers, lubricants,biocides, tints, antifoams, antistatic agents, antioxidants, etc.,present in known amounts in the emulsion. The polyester filamentsfollowing application will normally contain from 0.01 to 0.40 percent ofthe haloester organic compound and coreactant reaction product based onthe weight of the filamentary material; preferably about 0.1 percent.

After the haloester organic compound and the coreactant are applied, thepolyester filamentary material can be drawn or stretched to obtain adesired orientation. A total draw of from about 5.0:1.0 to about 6.5:1.0in a low birefringence process and from about 1.5:1.0 to about 2.8:1.0in a high birefringence (i.e., high stress) process is typicallyconducted in one or more drawing stages using known equipment such aspairs of skewed draw rolls.

The draw temperature is selected to yield the desired result. Forexample, in a high birefringence, two-stage draw process, the firststage can be conducted at a temperature below the glass transitiontemperature of the polyester (e.g., room temperature) as set forth inaforementioned U.S. Pat. No. 4,414,169. The second stage can also beconducted at a temperature below the glass transition temperature of thepolyester (e.g. at room temperature).

After drawing, the polyester filamentary material can be subjected to arelaxing step of from about 0 to about 4% and/or heat setting at fromabout 190° to about 240° C.

In a second aspect of the invention the haloester organic compound andthe coreactant can be applied as an emulsion or solution to thefilamentary material after the drawing process employing yarn heatingand the known techniques described above. Following application afterdrawing, the filaments will normally contain from 0.02 to 0.5 percent byweight of the aliphatic haloester organic compound and coreactantreaction product based on the weight of the filamentary material.

The surface-modified polyester produced by the process described abovecan be further processed to produce a material having utility in theproduction of tires and other articles of manufacture. Typically, in theproduction of such articles, a phenolic-aldehyde-latex composition isapplied to the polyester yarn. The phenolic-aldehyde component (e.g. aresole) can be any condensation product of an aldehyde with a phenolwhich can be heat cured to form an infusible material. A typicalphenolic-aidehyde-latex composition is a formulation containingresorcinol-formaldehyde resin and a rubber latex such asstyrene-butadiene vinyl pyridine latex (e.g., an RFL composition). Thepreparation of such compositions is well known in the art.

The phenolic-aldehyde latex composition is generally applied in aquantity of from about 2 to about 10 weight percent (solids retention),based on the weight of the polyester material. Although not to belimited thereto, the phenolic-aldehyde-latex composition is preferablyapplied after the filament or yarn has been twisted into cord or woveninto fabric. Preferably, the composition-coated material is subjected toa drying and curing treatment, both to eliminate the moisture in thecoating and to complete the condensation of the phenolic-aldehydecomponent. The drying and curing operation is conveniently conducted inthe presence of hot circulating air at a temperature of from about 120°to about 260° C.

The aliphatic haloester organic compound and the cationic compound canbe admixed with other agents to achieve desirable results. For example,they can be used to replace the glycerol epoxide in a suspension ofphenol blocked methylene-bis(4-phenylisocyanate) and applied to thepolyester in cord form in the first step of a two stage process asdescribed in U.S. Pat. No. 3,307,966. The RFL would be appliedseparately in a second stage.

The surface-modified polyester material onto which the RFL compositionhas been applied may then be used as reinforcing materials in thepreparation of reinforced rubber-based materials such as pneumatictires, conveyor belts, hoses, transmission belts, raincoats, and thelike employing methods known to the art.

The following Examples are given as illustrations of the invention. Itshould be understood however, that the invention is not limited to thespecific details set forth in the Examples.

EXAMPLE 1

A commercial 0.90 IV polyethylene terephthalate industrial yarn wastwisted into a 1000/2 12×12 tpi cord, and the cord adhesive treated on aLaboratory Litzler Computreater using a two stage process. In the firststage, the cord was stretched 3% and then passed through amethanol/water solution containing 1.08 parts of a chloro-ether-esterdescribed below, and 0.21 parts of potassium carbonate in 25 parts ofwater and 75 parts of methanol. The excess solution was blown off toachieve an application level of 0.2 dry weight percent on cord, and thenexposed for thirty seconds at 400° F. In the second stage, the cord wasrelaxed 3% and a RFL adhesive described below was applied to the cord toachieve 3.5% weight percent solids pick up, and the cord was exposed to450° F. temperature for fifty seconds.

The chloro-ether-ester used in the methanol/water solution consisted ofa diether of PEG200 diol with nominally two oxychloropropylene unitswith two terminal 1-glycerol ethers that have been fully esterified withacetic acid.

Analysis of the chloro-ether-ester showed it to have a chlorine contentof 10.23% and a low hydroxyl value of 21.6 mg KOH/g. 13C NMR showed onlya trace of hydroxyl groups and no detectable chlorohydrins. The moisturecontent was 0.02%, epoxy value was 0.19% (as C2H3O) and the sodiumchloride content was 0.07.

The composition of the RFL adhesive had the following ingredients:

    ______________________________________                                        Ingredients            Parts by weight                                        ______________________________________                                        water                  331                                                    NaOH (50% aqueous solution)                                                                          2.6                                                    resorcinol             16.6                                                   formaldehyde (37% aqueous solution)                                                                  17.2                                                   terpolymer latex of styrene/                                                                         245                                                    1,3-butadiene/2-vinylpyridine 15/70/15                                        (41% latex)                                                                   ______________________________________                                    

The above composition was prepared by adding the 2.6 parts of 50% NaOHto the water, followed by the 16.6 parts of resorcinol and 17.2 parts offormalin. This mixture was aged for one hour and stirred in to the 245parts of the terpolymer latex. The resulting mixture was aged for 24hours.

The treated cord prepared above was placed on a fabric backed rubberpiece by winding on a rotating rubber drum. The cord was placed as tightas possible an end count. The fabric was cut into two 3"×3" squares andthese squares were placed together, treated cord to treated cord, with arubber layer 0.040 in. thick in between. The samples were thenvulcanized at 320° F. for 13 minutes at 50 psi pressure, and thevulcanized samples were cut into three 1 in. strips.

One strip was placed in an environmental chamber at 220° F. for 30minutes, and then the fabric plies were pulled apart at 220° F. on anInstron tensile tester at a rate of 6 in./minute. A second strip wastested under ambient (22° F.) conditions. The adhesion is characterizedby the average force generated (pounds/inch) and by a visual rating. Thevisual rating is based upon a 1 to 5 scale where 1.0 is total failure atthe fiber surface and 5.0 is cohesive failure in the rubber compound.

For purpose of comparison, the same cord was treated in exactly the samemanner, except 0.290 parts of potassium acetate was used in themethanol/water solution rather than 0.20 parts of potassium carbonate.In each case this represents nominally two equivalents of potassium ionper mole weight of chloro-ether-ester.

The results of the adhesion testing are:

    ______________________________________                                                 22° F. Peel Test                                                                    220° F. Peel Test                                           Pull Force                                                                              Visual   Pull Force                                                                            Visual                                  Sample     (lb/in)   Rating   (lb/in) Rating                                  ______________________________________                                        CONTROL    17.4      1.4      7.0     1.1                                     PREFERRED  35.5      2.7      24.1    2.8                                     ______________________________________                                    

EXAMPLE 2

Molten polyethylene terephthalate (PET) having an intrinsic viscosity of0.928 deciliters/gram was spun at a temperature of 299° C. The productspun filaments were subjected to a two-stage drawing process with thefirst stage being conducted at ambient temperature and at a draw ratioof 1.2:1 and with the second stage being conducted with a steam jetbetween the draw rolls at 305° C. and a draw ratio of 1.6:1. The PETyarn was heat set at about 247° C. and then wound at a speed of 4760meters per minute to obtain a slight relaxation. The yarn was of 1000denier.

In this Example a blend was prepared containing 11.0 weight percent of amethyl ether containing nominally two oxychloro-propylene units withterminal 1-glycerol ether that is mono-esterified with an acetic acidresidue, mostly in the remaining primary hydroxyl position, 1.80 weightpercent of tetramethylammonium carbonate and 87.2 weight percent of amixture comprising organomodified silicone, ethoxylated sorbitanmono-oleate, ethoxylated octylphenol and other minor ingredients.

Analysis of the chloro-ether-ester showed it to have a hydroxyl value of149 mg KOH/gram, a total chlorine content of 24.46%, an epoxy value of0.18% (as C2H3O), an acid value of 0.25 mg KOH/g, a moisture content of0.06% and a sodium chloride content of 0.20%. A 13C NMR spectrumindicated that most of the ester acetate was attached to the primaryposition of the glycerol ether unit, and showed no detectablechlorohydrins.

The blend of surface-modifying chemicals as a 5% emulsion in deionizedwater was metered onto the filaments as they exited the solidificationzone and prior to drawing. The dry weight concentration of finish on theyarn after wind-up as determined by extraction with methanol was 0.40%which is representative of a reaction product concentration of 0.05%.

Cords were prepared from the drawn yarns, and then treated using a dippick-up of 6.5% target with a resorcinol-formaldehyde-latex (RFL)composition typically used in the tire industry.

After coating with the RFL, the coated cord was subjected to aconventional curing using a Litzler Computreater at standard conditionsfor tire cord. The treated cord was then tested for adhesion asdescribed in Example 1. Adhesion results are shown below.

    ______________________________________                                        Adhesion at 22° C.                                                                           Adhesion at 105° C.                              lbs/in  visual rating lbs/in  visual rating                                   ______________________________________                                        34.5    2.2           23.7    2.1                                             ______________________________________                                    

While the invention has been herein described in what is presentlyconceived to be preferred and exemplary embodiments thereof, those inthe art may recognize that many modifications may be made thereof, whichmodifications shall be accorded the broadest scope of the appendedclaims so as to encompass all equivalent methods and products.

That which is claimed is:
 1. A process which comprises contacting asurface of a polyester fiber with a chloroester organic compound and acationic compound selected from the group consisting of alkali metal,quaternary ammonium, alkali metal hydroxides, carbonates andbicarbonates, wherein the chloroester organic compound is represented bythe formula ##STR3## wherein R₁ is H or a C₁ -C₂₂ organic acid esterresidue; R₂ is a C₁ -C₂₂ organic acid ester residue; n is 0-10 and m is1-4 and R₃ is an organic residue of valence m, and to include a secondprocess step of further contacting the polyester fiber surface with aphenolicaldehyde-latex composition.